The present invention relates generally to the field of compressors of the scroll type. It is specifically directed to an element for effecting sealing between the axial tip portion of a scroll wrap element and the end plate of the opposing scroll member as well as to a method of injection molding such tip seal elements.
In scroll compressors, a drive motor typically drives one of the two scroll members that comprise the compression mechanism. Each scroll member has an end plate from which an involute wrap extends. The involute wraps of the pair of scroll members are interleaved and are constrained, by use of a device such as an Oldham coupling, to relative motion such that one scroll member orbits with respect to the other.
Such orbital motion, when in the proper direction, causes the cyclical creation of open suction pockets at the radially outward ends of the interleaved involute wraps of the scroll members. During compressor operation, such pockets fill with suction gas, close and are displaced radially inward, while decreasing in volume, thereby compressing the gas trapped in them. The compression pockets are ultimately displaced into communication with a discharge port, located at the center of the scroll set, and compressed gas is expelled therethrough.
Once closed off from the suction area but prior to being displaced into communication with the discharge port, the compression pockets formed by the scroll members must become and remain sealed if the compression process is to be efficient. Failure to control leakage from higher pressure compression pockets to lower pressure compression pockets or back to the suction area of the compressor decreases compressor efficiency. On the other hand, the use of excessive force to seal such pockets through direct contact of the surfaces of one scroll member with opposing surfaces of the other scroll member places an unproductive load on the compressor drive motor which likewise reduces compressor efficiency.
The sealing of scroll compression pockets is accomplished by the moving flank-to-flank line contact or near contact of the upstanding scroll wraps of the two scroll members as well as contact between the tip of each scroll wrap with the end plate of the opposing scroll member. Depending upon design choices made with respect to a scroll compressor, actual flank-to-flank contact may or may not be provided for. In so-called "fixed throw" scroll compressors the scroll wraps are aligned such that their flanks are maintained in near contact rather than actual contact.
Likewise depending on the design of the compressor, sealing between the tip of an involute wrap of one scroll member and the end plate of an opposing scroll member may be achieved by direct wrap tip to opposing end plate contact or by the use of a tip seal ensconced in a groove defined in the tip of the involute wrap. In most compressors, lubricant is supplied to the scroll set, most often carried in the gas undergoing compression or through a lubricant injection arrangement, to both lubricate the surfaces of the scroll members that are in contact with each other and to seal the compression pockets defined by the scroll members at their contact or at near contact locations.
U.S. Pat. No. 801,182 long ago disclosed the use of tip seals in scroll apparatus. U.S. Pat. No. 3,994,636 is illustrative of subsequent yet still very early developments relating to the use of tip seals therein. Both patents, which are incorporated herein by reference, suggest, among other things, tip seal elements fabricated from a single strip of material. The '636 patent suggests the use of both metallic and nonmetallic materials in tip seal fabrication. Both of these patents, however, predated by decades the introduction of scroll apparatus into large scale commercial production and, as such, were speculative in their teachings concerning tip seals and their design, fabrication and use.
U.S. Pat. No. 4,415,317, assigned to the assignee of the present invention and incorporated herein by reference, teaches a tip seal for scroll apparatus fabricated from a plurality of adjacent strips of material. The tip seal design of the '317 patent has proven to be both producible and effective in application and came to be used in among the very first scroll compressors manufactured for commercial use in the 1980's.
The '317 patent noted, at the time of its writing, that the use of a unitary piece of material to form a tip seal element, while seemingly advantageous in many respects, had drawbacks. Among those drawbacks was the fact that such pieces had to be machined or otherwise formed to the precise involute shape of the groove in the tip of an involute wrap in which they were required to be inserted in order to afford proper sealing. The '317 patent noted that the necessity for machining or other special formation of tip seals from a unitary piece of material brought with it disadvantages relating to the difficulty and expense of the machining operations involved or, in the case of the plastics then available, deficiencies associated with the elasticity and wearability of the material. The laminated tip seal of the '317 patent, which was comprised of side-by-side strips of steel, provided both the robustness and flexibility necessary to face the rigorous and relatively high temperature applications in which it was used.
More recently, newer engineered materials have been developed which have, in fact, permitted the fabrication of sufficiently flexible, robust and heat resistant unitary tip seals for use in scroll compressors that are moldable and do not require finish machining. Exemplary in that regard are the tip seals and teachings of very recent U.S. Pat. Nos. 5,575,634 and 5,636,976 which are likewise incorporated herein by reference.
The '976 patent is particularly noteworthy both with respect to the invention it claims and the art it describes in its "Background of the Invention" portion. In its "Background of the Invention", the '976 patent identifies the existence of Japanese patent documents related to injection molded tip seals, one such document (JP-A-4-262087) teaching, according to the '976 patent, a conventional method of manufacturing a tip seal with a synthetic resin where the synthetic resin is "supplied up to both ends of a mold for a scroll-shaped tip seal by providing a side gate, through which the synthetic resin is to be injected, on a side of the mold for the tip seal at the substantially intermediate portion of the entire length thereof".
The '976 patent goes on to state, with respect to that particular method of manufacturing, that "a convex portion m is formed as a gate trace on a side of a tip seal", that particular tip seal and concept being illustrated in FIG. 6 of the '976 patent. That convexity in the sidewall portion of the tip seal is said to adversely affect the sealing properties of such tip seals. That particular problem and adverse effect was solved, according to the '976 patent "by injection molding with a side gate provided at a portion which is an outside end of a mold for a scroll-shaped tip seal in a method disclosed in JP-A-6-137285, so that a sealing property of the tip seal is improved by preventing the formation of a gate trace on a side of the tip seal". The '976 patent then goes on to identify still other problems associated with methodology of JP-A-6-137285 and describes, as its invention, a tip seal and methodology to overcome those still other problems.
Despite all of these teachings, certain newer and even more advantageous "engineered materials" have been developed. These materials have characteristics which, while making them particularly appropriate for use in tip seal applications, are so highly viscous in the "fluid" state that they must be in to permit their injection into a mold cavity, that existing injection molding methodologies are incapable of permitting the fabrication of tip seals from such materials. This incapability results from a failure to be able to force the base material completely into the small cross-section (often nominally 0.01 square inches or so), relatively very long (on the order of one foot) involute-shaped cavity that the mold for a single piece tip seal must define.
As such, the need exists for economical single piece tip seals manufactured from engineered materials having superior wear and heat resistance characteristics to those of existing tip seals and for a methodology of forming such tip seals through an injection molding process.